I loved this article about 7 beautifully bizarre beaches around the US and elsewhere [link].  In particular, of relevance to Hawaii:

1. Red sand, Kaihalulu, Maui, Hawaii
When a a breach in the Earth’s crust lets loose a geyser of magma, the volcanic ash and material has to go somewhere, and, quite often, forms a massive conical structure called a cinder cone. At Kaihalulu Beach, an ancient cinder cone crumbles into a bay as the tide erodes it further, ensuring its inevitable total destruction. In the meantime, the sediment from the cinder cone forms this beach of red sand.
Photo: xoque

2. Green sand, Papakolea, Hawaii
Likewise, at the nearby Papakolea Beach, another cinder cone rich in olivine minerals — a common component of Hawaiian lava — spills forth a surreal pasture of dark green sand. The beach is found at the end of a long hike on the south of the Big Island.
Photo: Wikimedia Commons

The other beaches are in California, Bahamas, and Greece.

Source for this content:

http://matadortrips.com/photo-essay-7-beautifully-bizarre-beaches